@Boudewijn an option could be (may only as gold member) to save the route as .pdf
May this will not support your needs exactly.
I believe, it will not be an easy development, to generate out of route data a roadbook (in Rallye style). There are several specialised tools on market, to do this. They will probably have a big head start in development.
On the other side: to populate out of the generated data an applicable PDF document would also be not that easy. Because typically a roadbook document must be in a dedicated format.
If you have got a ready to use pdf-roadbook, you should have a bigger screen to view it (during ride). It's not that easy to view it - nor to operate it - during ride at a little smartphone. And in best way, you should have a remote controller button at the handle bar of you bike.
For such a purpose, I'm using the DMD2-App on a T865-X device from same manufacturer. On this device (Android based) you can run several other Apps to - like MyRoute-App.